This invention relates to medical implants to be implanted around a patient's tissue structure, body conduit, or organ. An illustrative use of the invention is implanting one or more of such implants around a patient's stomach to treat obesity.
Surgical intervention for the treatment of obesity is already in practice. Patients with a body mass index (BMI) greater than 40, or a BMI greater than 35 but with one or more co-morbid conditions are currently candidates for surgical intervention. In addition, there is ongoing research related to patients with lower BMI (e.g., 30-35) to determine the risk/benefit of using these therapies in such patients. In general, as the BMI threshold is lowered, the therapy risk profile must be reduced because this patient population has less benefit to gain. Gastric bypass and gastric banding are the two most common procedures performed.
Conventional gastric banding involves the placement of a rigid ring (often with an inflatable member on the inner surface of the ring) around the outside of the stomach to create a small conduit or stoma between the proximal and distal stomach. This restriction serves to slow the rate of food passage through the stomach, increasing the patient's feeling of fullness, thereby reducing food intake and resulting in the patient losing weight. The inflatable member (if included) allows the stoma to be adjusted smaller or larger in diameter by adding volume to or subtracting volume from the inflatable member in response to inadequate weight loss, stoma obstruction, patient symptoms and tolerance, etc. The adjustment is often accomplished through a fluid-filled reservoir and port, which are implanted in the patient's abdomen. One common way a physician can add or remove fluid is by accessing a port beneath the patient's skin, e.g., by injection with a syringe. In another method, the stoma adjustment is accomplished through an expansion of a polymer material, which is activated by mechanical means to increase or decrease the extent of the restriction. In either case, adjustments are made based on caregiver interaction and are in response to balancing the need to accelerate/maintain weight loss in relation to patient discomfort.
In general, known gastric banding techniques are reasonably effective in causing weight loss. The known technologies are, however, subject to certain drawbacks. One drawback is that implantation of a fluid reservoir can be associated with infection. Another possible drawback is that adjustments performed by injection with a syringe can lead to punctures of the port and/or tubing, causing loss of the contained fluid and rendering the treatment ineffective. Additionally, gradual loss of pressure due to osmosis of fluid from the inflatable member can necessitate regular interventions to adjust the diameter of the ring (gastric band).
Another possible drawback of conventional gastric banding is due to the nature of its fixed stoma or constriction. It has been noted that patients who consume their food by drinking high calorie sweets, liquids, or soft foods do not benefit substantially from treatment with a gastric band. Furthermore, patients are encouraged not to drink liquids with food because this has been shown to speed up digestion and passage through the stoma, which can limit the effectiveness of gastric banding.